The problem of separation of the base oil (oil separation) from the electroconductive grease under high temperature directly affects the life span of practical machine bearings. Therefore, improvement of this problem is desired. Expecting the thickening effect of electro conductive materials, there are two-components system electroconductive greases. For example, Patent Document 1 proposes one comprising a fluorine base oil and a carbon black thickening agent; however, in order to overcome the problem of oil separation, PTFE must be mixed into this grease.
Therefore, Patent Document 2 proposes an electroconductive grease comprising a base oil (e.g., fluorine oil), a PTFE thickening agent, and 0.2 to 10 mass % of carbon black. The correlation between the DBP oil absorption amount of the carbon black used and the maximum bearing resistance indicates that the DBP oil absorption amount is preferably 180 ml/100 g or more in the range of 110 to 300 ml/100 g. However, Patent Document 2 does not provide any description of the properties and proportion of the PTFE thickening agent used.
Further, Patent Document 3 proposes a grease composition comprising a base oil comprising a synthetic oil and a fluorine oil, and a thickening agent comprising carbon black and PTFE in an amount of 5 to 40 wt. % based on the total mass of the grease, wherein the proportion of the carbon black and the PTFE thickening agent is 20:80 to 60:40 (mass %), and the carbon black has a DBP oil absorption amount of 100 ml/100 g or more. However, Patent Document 3 nowhere refers to the properties of the PTFE thickening agent used.